1. Field of the Invention
The present invention relates to symmetrical naphthalenetetracarboxylic acid diimide derivatives and to a photosensitive material for electrophotography which contains a naphthalenetetracarboxylic acid diimide derivative as an electron transporting agent and is used for the electrophotographic copy, printer and common paper facsimile.
2. Description of the Prior Art
In an electrophotographic method, an electrophotosensitive material is electrically charged and is exposed to image-bearing light to form an electrostatic latent image which is, then, developed into a toner image in a state where a developing bias voltage is applied, and the formed toner image is transferred onto a transfer paper or the like paper and is fixed to form an image. This electrophotographic method is extensively used for the digital or analog copy, printer and common paper facsimile.
A selenium photosensitive material and an amorphous silicon photosensitive material have heretofore been used for the electrophotography. In recent years, however, an organic photosensitive material (OPC) has also been extensively used. Representative examples of the organic photosensitive material include a laminated-layer photosensitive material of the separated function type in which a charge-generating agent (CGM) and a charge-transporting agent (CTM) are laminated one upon the other as separate layers, and a single-layer photosensitive material in which the CGM and the CTM are formed as a single dispersion layer.
As the charge-generating agent, there have been known a variety of inorganic or organic charge-generating agents such as selenium, selenium-tellurium, amorphous silicon, pyrylium salt, azo pigment, disazo pigment, trisazo pigment, anthanthrone pigment, phthalocyanine pigment, indigo pigment, threne pigment, toluidine pigment, pyrazoline pigment, pyranthrone pigment, perylene pigment and quinacridone pigment. As the charge-transporting agent, there have been known positive hole-transporting agents such as poly-N-vinylcarbazole, phenanthrene, N-ethylcarbazole, 2,5-diphenyl-1,3,4-oxadiazole, 2,5-bis-(4-diethylaminophenyl)-1,3,4-oxadiazole, bis-diethylaminophenyl-1,3,6-oxadiazole, 4,4'-bis(diethylamino)-2,2'-dimethyltriphenylmethane, 2,4,5-triaminophenylimidazole, 2,5-bis(4-diethylaminophenyl)-1,3,4-triazole, 1-phenyl-3-(4-diethylaminostyryl)-5-(4-diethylaminophenyl)-2-pyrazoline, p-diethylaminobenzaldehyde-(diphenylhydrazone), tetra(m-methylphenyl) methaphenylenediamine, N,N,N',N'-tetraphenylbenzidine derivative, N,N'-diphenyl-N,N'-dixylylbenzidine, as well as electron-transporting agents such as 2-nitro-9-fluorenone, 2,7-dinitro-9-fluorenone, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2-nitrobenzothiophene, 2,4,8-trinitrothioxanthone, dinitroanthracene, dinitroacridine, dinitroanthraquinone, naphthoquinones, and 3,5-dimethyl-3',5'-di-t-butyldiphenoquinone.
U.S. Pat. No. 4,442,193 discloses a photoconducting composition containing a photoconducting material and a 1,4,5,8-naphthalenebisdicarboxyimide derivative sensitizing compound.
U.S. Pat. No. 5,468,583 discloses a photoconducting element comprising an electrically conducting layer, a charge-generating layer and an electron-transporting agent in a polymeric binder layer, wherein the electron-transporting agent comprises at least one kind of a cyclic bisdicarboxyimide represented by the following formula (2), ##STR2## wherein Q1 and Q2 may be the same or different and are each a branched-chain alkyl group, an unsubstituted straight-chain alkyl group, an unsubstituted cyclic alkyl group, an alkyl-substituted cyclic alkyl group, an unsubstituted straight-chain unsaturated alkyl group, an aryl group, an alkyl group having 2 to 20 carbon atoms, an alkoxyl group or a hydrogen atom, and wherein Q1 and Q2 are not hydrogen atoms simultaneously, and R1, R2, R3 and R4 may be the same or different and are each a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an alkoxyl group having 1 to 4 carbon atoms, or a halogen atom.
Japanese Examined Patent Publication (Kokoku) No. 39098/1989 discloses an electric semiconductor or a photoconductor comprising naphthalenetetracarboxylic acid diimides represented by the following formula (3) ##STR3## wherein R is a saturated or olefinically unsaturated aliphatic or alicyclic group which includes an electron-donating group, and R1, independently from each other, is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a halogen atom, NO.sub.2, SO.sub.3 H, CN, COOR.sub.2, NR.sub.2 (wherein R.sub.2 is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms), a hydroxyl group or an alkoxyl group having 1 to 4 carbon atoms.
Among the charge-transporting agents, however, very few electron-transporting agents are satisfying a practicable level, and further improvement in the performance is desired even with respect to photosensitivity.
The naphthalenetetracarboxylic acid diimide derivative is a promising compound as an electron-transporting agent but is not still satisfactory concerning solubility in an organic solvent and compatibility with a resin binder that is used, and tends to be precipitated in the form of crystals in the photosensitive layer and in the electron-transporting layer, deteriorating the electrophotographic properties of the photosensitive material.
When used at a concentration that maintains compatibility with the resin, furthermore, the naphthalenetetracarboxylic acid diimide derivative exhibits insufficient photosensitivity. It is therefore desired to increase its photosensitivity.